The Conservatives today criticised the government for failing to support proposals from a number of African countries to impose a 20-year ban on any legal sales of ivory.

The plan, led by Kenya, is being discussed at the meeting of the Convention on International Trade in Endangered Species (Cites) in a bid to tackle the poaching of elephants and rhino.

It counters a bid by Tanzania and Zambia to hold one-off sales of their legally held ivory and "downlist" their elephants from the highest level of protection.

The UK government said it was initially "sympathetic" to the Kenyan proposals, subject to a review after 10 years of the scheme, but the EU, which votes as a bloc at Cites, decided not to back it. But on a Cites vote this week on whether to ban the international trade in bluefin tuna, the UK acted alone rather than as a bloc with Europe and chose to support the Monaco proposal of opposing the ban.

There are concerns that, if the one-off sales of ivory from four African countries in 2008 results in a lower demand for illegal ivory, a 20-year moratorium would not be a positive step.

But conservationists have raised fears over a rise in illegal trade and poaching following the sales, which they believe stimulate the market and provide a cover for traders to offload illegal stocks.

Shadow environment secretary Nick Herbert said the government had "shamefully" refused to support the Kenyan proposal for a ban on sales and continued to back stockpiling of legal ivory - for example from animals which had died naturally.

"Instead of flooding the market with more ivory and legitimising the trade, these stockpiles should be destroyed. We should be choking demand for ivory, not stoking it," he said.

The UK opposes the bids by Tanzania and Zambia to have one-off sales of their ivory, but EU countries are still considering their requests to "downlist" their elephants from Appendix I to Appendix II of the convention.

Such a move would not allow a trade in ivory, but could let other elephant body parts be traded internationally and the sale of live elephants, for example to safari parks elsewhere, could go ahead.

It could pave the way for a potential ivory sale in the future.

A Department for Environment, Food and Rural Affairs (Defra) spokeswoman said: "The EU has agreed with the UK's position to vote against the proposals from Tanzania and Zambia to sell ivory stocks in a one-off sale.

"The EU has decided not to support Kenya's proposal for a moratorium of ivory sales for 20 years."

She said that, regardless, the UK would not consider other sales of ivory until the effects of the 2008 one-off sale of ivory, which was intended to reduce demand for illegal poached ivory, had been fully analysed.

That would take at least another six years, she said.

The 20-year ban would extend an existing nine-year moratorium, agreed at the time the four African countries were given the go-ahead to sell their legal ivory stocks, on any further sales.